Recent significant outcomes

THREE DISTINCT RADIOELEMENTAL AND RADIOGENIC HEAT PRODUCTION ZONES IN THE BUNDELKHAND CRATON, CENTRAL INDIA

(Ray et al., Int. Jour. Ear.Sci. 2016)

The granitic rock is an important component in understanding the crustal evolution in a geologic province. Radioelemental (232Th, 238U, 40K), petrological and geochemical analyses on granitoids and gneisses of the Bundelkhand craton, central India reveal following significant results:

  • Three types of Bundelkhand granitoids (i.e. K-feldspar rich pink granitoid: PG, biotite rich granitoid: BG and Na-feldspar and mafic minerals rich grey granitoids: GG) and two types of gneisses (i.e. potassic and sodic types, BnGC-I, II)  show distinct radioelemental (Figure 1) characteristics.

 

Figure 1: Average and standard error (s.e.) in (a) Th, (b) U, (c) K and (d) heat production  for the Bundelkhand granitoids (PG, BG and GG) and Bundelkhand gneissic complex (BnGC-I, II).

  • The craton can be divided into three distinct radioelemental zones that can be correlated with its evolution in time and space. The central part is characterized by lowest, the southern part is characterized by highest, the northern part is characterized by moderate radioelements (Figure 2). These differences could be attributed to the compositional different magma sources from which they were evolved. 

 


Figure 2: Three distinct radioelemental zones in the Bundelkhand craton, central India

THERMAL CONDUCTIVITY ESTIMATION OF GRANULITES FROM MINERALOGY OF ROCKS
(Ray et al., Geothermics, 2015)

Granulites are important parameter to constrain temperature distribution of crustal and sub-crustal lithosphere in any geological province. But most of the thermal models are confronted with the problem that either non-availability of the exposed lower crust or non-availability of proper samples for laboratory measurements. Study shows that in case of non-availability of samples for laboratory measurement, mineralogical data can be used  for estimation of thermal conductivity with proper precaution.

Thermal conductivity of various types of the granulite rocks, e.g., felsic, intermediate and mafic granulites, have been measured in the laboratory by the steady-state method and the optical-scanning method. These are also calculated from modal mineralogy (determined by XRD and EPMA), applying several mathematical mixing models that are commonly used in thermal studies and mineral thermal conductivity. Different models are related with the measured values as: lm < lHM <lGEO< lLHS< lHHS< lEFF<lAM , where lHM , lGEO, lLHS, lHHS, lEFF, lAM: Harmonic, geometric, lower and upper Hashin-Shtrikman mean, effective, arithmetic means.

Study shows that considering mean mineral thermal conductivity, harmonic mean provide best fit values between estimated thermal conductivity and measured thermal conductivity (Figure 3).


Figure5rev.tif


Figure 3  Deviations between measured and calculated bulk thermal conductivity for different mixing models. Calculated thermal conductivity, based on the minimum, mean and maximum mineral thermal conductivity, are shown by green line, grey shaded and dotted red bars.

Ongoing Projects:

Project Title Project Number & Sponsored by

Heat Flow, Heat Production and Crustal Thermal Structure in the Indian Shield

MLP-6503-28 (LR)

Delineation of areas with anomalous high temperatures towards exploration of non- conventional geothermal energy resources.

SHORE (PSC – 0205)

Staff:

Name Designation
Dr. Labani Ray

Senior Scientist and Project Leader

Mr. G. Ravi

Technical Officer